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Upgrading the RS Musical Instrument Cab to a Bass Cab

Discussion in 'Amps and Cabs [BG]' started by Thor, Apr 11, 2005.

  1. Thor

    Thor Gold Supporting Member In Memoriam

    As noted above, it was suggested by Bill Fitzmaurice that additional internal bracing was in order.
    I constructed a small panel from a piece of scrap maple plywood. I fit the panel carefully. I also cut little cleats to help attach the panel internally. Here is an intermediate fitting and pics of the work done recently:


    Here is a closer look at the panel. Note that I made small channels in the side to allow the wiring to pass through.


    Attached Files:

  2. Thor

    Thor Gold Supporting Member In Memoriam

    In the event this ends up being a ported cabinet upgrade, I added air flow vents to the brace to allow air to flow
    freely between the 2 speaker 'compartments'. I happened to have a jig available for placing and cutting holes for doorknobs, but any circular hole saw would be fine.


    I added an additional channel by drilling two 1 1/4" holes and
    sawing out the center with a jig saw.


    Here is a picture of the final fit. Looks good. It is now ready to be glued up after I receive the speakers and
    recheck the fit of everything.


    Next comes the most difficult part, the speaker selection research. I obtained a copy of bgavins driver spec sheet
    and am in active discussion over specs of drivers pro and con.

    With unlimited funds, driver selection wouldn't be such an issue. In the real world, we often have to make compromises, and as such, I have set a limit of about 200 dollars for the drivers, shipped. Cheaper would be better, as well, to the point where one buys 'too cheap' with the resulting inferior quality and poor performance.
    Last edited: Dec 5, 2014
  3. Petebass


    Dec 22, 2002
    QLD Australia
    I can't see the pics, but I have had this same trouble with my PC before. Can everyone else see them OK?
  4. Danm


    Sep 24, 2003
    Canberra Australia
    Yes we can Pete,

    You might try putting your mullet on the right way this morning so that you can see....
  5. Petebass


    Dec 22, 2002
    QLD Australia
    I'm on the work PC now and I can see the pics. The home PC must have something wrong with it. Sorry! Carry on.........
  6. Thor

    Thor Gold Supporting Member In Memoriam

    Well, let's knacker on to driver selection.

    I found this driver from the guy selling the used JBL's on Ebay. He now reps this line in the US.
    The name of the company is Assistance Audio in Utah.


    The specific driver I was looking at was the 12.75 W1

    Unfortunately, I can't access the specs at the Ciare website, as the Macromedia Flash gizmo stuff goes crazy.I emailed for the T/S parameters to the rep.

    I also sent a note to Petebass to see if he could access them. Or load them up to WinISD. Which is the least he can do after knackering the thread .... :p

    The 108 price tag plus 20 shipping is pretty close to where I need to be, and it seems pretty high quality, a 3" voice coil, and I think a cast aluminum frame. ( Can't see the mechanical spec area on Ciare, either). As soon as I get the specs, I'll get them run for a 2 speaker config, 3.75 cu ft, with 3 ports of 2.75 inches.

    We'll see what happens.

    Edit: The Ciare 12.75 W1 spec'ed well as a midbass
    driver, but not well as a sub-bass driver.

    Also the 12.00 SW below it, though WAAAAAY to big for this, looks like one monster driver for the price of 161.00.1000 watts, 4" coil. (Maybe I'll start another project). :meh:
  7. Funkengrooven

    Funkengrooven Turn it down? You gotta be nuts!!

    You might find (or you might not) that the SWR 10's you just bought in a moment of drooling lust are made by Professional Audio Systems
    for spec's i think.
    Watch the drool, it rusts the frames....
  8. Thor

    Thor Gold Supporting Member In Memoriam

    I made a phone call to SWR ( Fender) Customer Service.

    Get this, all the replacement drivers are made by Eminence. Drum roll please .... Thanks. No PAS drivers in the new stuff. :bawl:
  9. Thor

    Thor Gold Supporting Member In Memoriam

    Ok, I pulled trigger on the Eminence Delta 12 LF's.

    I searched high and low and this one had the best specs for the budget I am on. I have come to the conclusion that I cannot get a cast frame driver that meets the specs for under a hundred dollars. No point chasing that, it is not going to happen.

    Even used JBL 2206 H models were going for 300+ for the pair on Ebay. My feeling is that this box is not perfect, and if I was going to buy those, I would build a new cab for them.

    Maybe later, after the college bills are paid off.

    Then when I went to buy them, NO ONE actually had them in stock. A phone call finally to Eminence got me a number of dealers nearby and a distributor on Long Island - that
    would not sell me direct. None of the people in this area that they dealt with stocked it, and none I spoke to would even drop ship it, most wanted me to pick it up after I ordered it.

    Avatar had it in stock, but would only ship by Fedex Ground. That's nice but they are in Idaho. To go there, find the buck-end of the planet, and take a left. No shipping options?
    Welcome to 1970!

    I finally called Low Down Sound in Ferndale MI and the 2 guys there, Bob and Ryan, hooked me up after I explained the problem, and the price I needed. I paid $70 per and
    a total shipping charge of $13 for a $153 delivered cost.That was a very fair price. And they had it drop shipped from their distributor directly to me, saving 4 or 5 days and extra freight costs.

    It was really nice to deal with some clever and creative guys who could get the job done. They made it easy to part with my cash when I was ready to buy, which is the way it should be. Kudo's to those guys, I am sure I will be sending more business their way. I like they way they do business.

    So the dirty deed is done, now I am waiting for them to show up, probably after this weekend.

    EDIT: LDS no longer has a store in MI. They still exist but I could not say if they do this anymore. Dave at Avatar has likely improved on shipping by now.
    Last edited: Dec 5, 2014
  10. Funkengrooven

    Funkengrooven Turn it down? You gotta be nuts!!

    Well now it seems that I won't get 30 emails a day with speaker questions...I don't know whether to be relieved or lonely.... :D
    good luck and let me know how they sound...
  11. Petebass


    Dec 22, 2002
    QLD Australia
    Not quite. We haven't worked out the porting yet :)
  12. Thor

    Thor Gold Supporting Member In Memoriam

    I picked up 3 of these ports, they fit the 2 upper holes perfectly. They are the same ones which I am using for the Hardcore (Moskowitz) cab I am building at the same time. A third port can be accommodated pretty much anywhere on the front panel.

    There is a little bit of a grid at the back of the ports, to keep evil sounds from escaping from the cab, and to keep small rodents from getting in.

    Ports from Simply Speakers.

    I am kind of a stickler on having things look right, so I may spray the ports with the Model Master Metalizer spray paints and install T nuts and stainless cap screws. Everything rusts in my neck of the woods, so I have used only stainless hardware for a few years now.

    I will run WinISD again over the weekend and double check all the numbers. If the tube lengths need to be changed, I will saw off the back and reglue the little grids back on.
  13. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    Next project, or even this if you need more stuff, try Parts Express. Prices are no more than half what you paid.
  14. Funkengrooven

    Funkengrooven Turn it down? You gotta be nuts!!

    Oh, Good Grief...I forgot the ports !!!
    Help me Rhonda....

    Rhonda?? .......Are You there??? Rhonda??? :crying:
  15. Thor

    Thor Gold Supporting Member In Memoriam

    :D I DID check them!

    The Delta 12 LF's are $96.99 from P.E., and the ports are 3" ( slightly too big for retrofit), part 268-350, flared, cost $10.65. I paid 5.65 each from Simply Speakers. I called them with the order, and the shipping of 3 of those, and some speaker clamps, was 8 dollars. (If you buy it on the web site they charge 25 bucks shipping. Which is why I called, as that way I could negotiate a better price.)

    Do you find you do better if you call Parts Express?

    OTOH, they may give you a much better price since you are in the trade :eek: , I don't know. You certainly buy a lot more stuff than I do.

    Attached Files:

  16. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    I couldn't make a direct comparison on the ports as I didn't know exactly which ones you ordered, but there are quite a few items there that are a lot cheaper at Parts Express for the identical piece. For instance their $8.95 SH3005 handle is $2.50 at PE (260-711) and $16.95 T-123 tweeter is $11.60 at PE (270-055). These are regular catalog prices. I don't automatically order from PE either, but they usually are very competitive and have a massive inventory, and often a somewhat higher price on one item is offset by a lower shipping charge if you order it all from the same place.
  17. Thor

    Thor Gold Supporting Member In Memoriam

    You are correct there.

    I sourced all the parts for the 'Len Moskowitz' cab I am building for a very compact home practice rig utilizing the Peerless 831759 driver and the Peerless 831646 mid recently, and found it virtually impossible to find the parts I needed from any one source. Shipping charges became a significant cost in the project as a result.

    I am actually documenting that build now as well for another thread, so eveyone can see what a hack I am. :oops: You learn by doing, and immersing yourself into these projects.

    I only bought the ports down there, as I already had one for the Moskowitz cab, and it retro fits perfectly into the existing tweeter holes at 2.75" diameter and length of 5.25 inches. The part numberis PT - 306. I bought 3 expecting I would need at least that many, so I have 4 total available.

    I will run the WinISD program again over the weekend and make some more measurments of the internal bracing to refine the total volume figure.

    I spent last night re-reading Vance Dickason's Loudspeaker Design Cookbook, the chapter on vented box design, so now I have a headache. :help: This is all starting to make more sense.

    Thanks again for your help!

    Attached Files:

  18. Wow, this brings back memories. I built a pair of speakers from the RS book back in 1980 or so, using drivers scrounged from a tube "hi-fi" system that my parents had bought in the 50's. Wasn't even stereo, just a mono phono amp and a mono powered extension cabinet.

    In hindsight, I wish I had kept the tube amps...
  19. Thor

    Thor Gold Supporting Member In Memoriam

    Here are some updates of the work completed since the last post.

    I removed the Radio Shack drivers. When I fitted up the Delta 12 LF's, it turned out that the mounting circle was slightly smaller than the old speakers. The Delta LF's have a circle of
    11.6300 inches and the RS drivers were 11.7500 “. That was just enough to make the screws splay out and not grab the T- nuts.

    Re-drilling the holes didn't seem a good option as the MDF can get a bit crumbly, so I solved it by drilling out the existing mounting holes to 5/16, gluing in 5/16 dowels cut flush to the baffle and letting it set over night.



    I then marked and drilled the new holes and installed and fitted both drivers.



    Last edited: Dec 5, 2014
  20. Thor

    Thor Gold Supporting Member In Memoriam

    Next, I removed the drivers and set them aside while fitting the rest of the parts, so they don't get damaged. I have come to the conclusion that it is best to fit all the pieces first before bolting it all together. So I have fitted and checked each sub-assembly against the whole. Then it will all gel
    together at once.

    I thought it really looked best, as in the above pic, when all three ports were together. I decided then to pull out the tweeter, and relocate all three tweeters to a vertical array on the front baffle, based on the vertical versus horizontal discussion in the first few posts of the thread. After careful measurement, loading the tweeters rotated 45 degrees from horizontal seemed to provide the best fit.

    The holes were then cut in the front baffle with a jigsaw, and T-nuts were installed to hold all the tweeters on.



    The center tweeter is going to interfere with the internal bracing, so that will have to be modified next to accommodate this new configuration.

    Looks like with a few more days of rain out here, I will be pretty close to being done.

    Attached Files:

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